Sprints and Muscle Growth

Question: I recently came across the following comment on Bret Contrerasí blog with regard to a figure athlete he is training and a question about sprintingÖ.

ďI donít have her do sprints. I have journal research that shows that sprints interfere with biochemical pathways involved in muscle growth. While sprints will help pack on mass for beginners, it can actually negatively impact more advanced lifters in terms of hypertrophy. Thatís why the bodybuilders donít sprint or do plyos Ė the risk isnít worth the benefits.Ē

The comment did not specifically cite the particular research, nor did it make mention of the sort of volume and distance of the sprints, i.e. whether this was low or high volume and whether the sprints were somewhere in the 10-40 yard range or beyond that range.

To the best of your current knowledge, is there a legitimate reason (biochemical or otherwise) why sprints would interfere with muscle growth? (I realize that with specific parameters and context this may be a bit tricky to tackle) I am not necessarily arguing that figure athletes or bodybuilders need to be or even should be performing them, simply wondering if those who may do so would actually be compromising results as Bret seems to intimate.

Answer: The short answer to your question is that Bret is right; certainly distance probably will have an impact but when people talk about ísprintingí for bodybuilders, itís usually some form of high-intensity interval training (HIIT) being discussed. That is, longer repeats (typically in the 30-90 second range). Few would be doing short sprints like a track sprinter.

As to the mechanism, Bret is most assuredly referring to AMPk (adenosine monophosphate kinase) and how it impacts on muscular metabolism. I wrote an article years ago about AMPk: Master Metabolic Regulator and talked about it in some detail in the Methods of Endurance Training series.

AMPk is activated, essentially, by alterations in the energy state of the cell: things that occur in both endurance training and longer sprint type training (AMPk is regulated both by the duration and intensity of activity). Activation of AMPk has a number of implications: itís involved in the adaptations to endurance training (stimulating various improvements to occur in the fibers in which AMPk is activated), increased fat burning, insulin sensitivity and a host of others.

Relevant to this specific issue, activation of AMPk has been shown to directly inhibit a molecular marker called mTOR (which stands for the mammalian target of rapomyacin, arenít you glad you know that now ). mTOR is a key player in muscle growth; for example, the amino acid leucine that so much has been talked about acitvates mTOR directly and this appears to be the major way that leucine/BCAA turns on protein synthesis.

So when you activate AMPk, via long-duration and/or high intensity endurance/interval training, this inhibits mTOR activity; inhibiting one of the prime players in muscle growth. Again, thatís surely what Brett is referring to.

Now, as you bring up, this probably doesnít hold for very short sprints but those would be uncommon for bodybuilders or physique athletes to do in the first place. For the type of sprint/interval training commonly advocated for such athletes, I agree that the negatives would outweigh any potential positives when maximal muscle growth is the goal (interval training can have potential benefits for fat loss, including stubborn fat loss, as discussed in The Stubborn Fat Solution).